Universal Serial Bus (USB) is an industry standard that defines the cables, connectors and communications protocols used in a bus for connection, communication, and power supply between computers and electronic devices. USB was designed to standardize the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electric power. It has become commonplace on other devices, such as smartphones, PDAs and video game consoles. USB has effectively replaced a variety of earlier interfaces, such as serial and parallel ports, as well as separate power chargers for portable devices.
A new USB Power Delivery Specification has been developed to enable delivery of higher power over new USB cables and connectors. This technology creates a universal power plug for laptops, tablets, etc. that may require more than five volts using cables and plugs compatible with existing USB solutions. The USB Power Delivery (USB-PD) Specification defines a packet-based communication link between ports connected via a USB-PD cable and USB-PD connectors. The packets contain information that enables the two ports to communicate and negotiate a voltage and a current that the source port will provide to the sink port. This communication occurs on a separate wire independently from the normal USB communications that appear on the USB data wires.
It has been proposed to incorporate an in-line transceiver inside a USB-PD cable as a way of communicating information about the cable to USB devices that the cable is connected to. Such an in-line transceiver illustratively would include or be associated with a non-volatile memory that stores information that the transceiver can send to such connected devices. In most embodiments, the in-line transceiver would be coupled with an embedded processor. Some examples of information that could be stored in the memory and transmitted to connected devices include: current and voltage capabilities of the cable, the cable manufacturer, the length of the cable, and an indication of whether the cable is active or passive. However, adding a transceiver inside the cable means that there are multiple possible destinations for any message sent by one of the three transceivers now associated with the cable (one at each end plus the at least one in-line transceiver). Thus there is a need for a simple and efficient means for a transmitter and a receiver to distinguish intended recipients of a transmitted message.